Even after reading her biography, I'm still not convinced that she actually invented, or even worked on the technology. I find it much more likely that she either funded the patenting process, and in this way got her name on the application, or that the "co"-inventor put her name on it out of admiration, thereby securing interest in the patent thanks to Lamarr's fame.
Edit 3: TL;DR - in many ways, it's Lamarr's part of the invention that is still in use today. The implementation produced by Antheil (and Mackowen) was basically rejected by the military as being impractical for their applications (it involved pneumatics, though there are disputes about the reasons for disinterest, at least at first, by the military). People who had worked on related ideas earlier, and even concurrently, had tried things like "wobbling" the signal, or moving in frequencies in other ways. AFAIK, the truly novel art and most important idea here, is "prearranged sequence of frequencies", a very "digital" (i.e. "discrete") and "programmatic", essentially, idea for the time. This was even before the Colossus computers and ~concurrent with creation of devices like the "Enigma" machines ... having forms of "programmability", more "digital" types of operation, etc. I don't think it's easy to be certain of many aspects of what exactly happened, but I do think crediting Lamarr for this invention is very clearly warranted, based on my knowledge of events.
It's an interesting enough story, IMO, to try to clarify this to the degree possible (or, at least, degree I can from my understanding):
First, Lamarr very much was an inventor. She was creative and continuously proposed, and in some cases produced, inventions.
Concerning frequency-hopping signals, she is the origin of the idea in the late 1930s in an arc that would produce a working method. She had several key insights and motivations that underlie her significant role in developing the idea into an actual "invention" (something with a practical demonstrated method of implementation):
1) She was aware, from direct interaction with Axis weapons manufacturers in the late 1930s, that they were devoting significant effort to intercepting and jamming Allied signals, including / in particular signals used to control weapons
2) She realized that having a prearranged sequence of frequencies, that a transmitter and receiver hopped between, should be workable / within reach
3) And, as regards motivation and commitment to ideas like this, in general - she was grateful to have been accepted in the US after fleeing Austria ... and not merely accepted, but have the career opportunity in Hollywood that she was building (though she was still angered there by being treated often as a "pretty face" rather than skilled / talented person / actress), and had an extremely strong drive to contribute to the war effort.
Her general knowledge of the practice and mathematics of frequencies, "carriers", signals, etc. contributed to her continued pursuit of the idea. She knew the base of it was solid, and I think she astutely judged that there ought to be some practical way of implementing it with technology available at the time in approximately the relevant footprint for some of the applications of most interest.
As for the basis of the practical device, that idea came from George Antheil. Antheil and an engineer at CIT (Samuel Mackowen) were then able, to create an entirely workable system and submit for and be granted a patent, which did include Lamarr (under her married name, and, actually did not include Mackowen - there's some interest in this as well, but, I guess he served as more of a consultant than originator of anything of enough note). Her key insights formed the basis for the work, although it seems likely she didn't contribute much to the practical implementation.
Finally, it should be noted that, as with many inventions, she was hardly the first person to play around with these sorts of ideas. Several others had experimented with the idea or related ideas, going back even 35+ years. But, she and her co-inventors came up with the abstract implementation (+ practical demonstration) / "blueprint" underlying a vast array of modern communications technologies.
Even after reading her biography, I'm still not convinced that she actually invented, or even worked on the technology. I find it much more likely that she either funded the patenting process, and in this way got her name on the application, or that the "co"-inventor put her name on it out of admiration, thereby securing interest in the patent thanks to Lamarr's fame.