Thinking about it you could do it this way :
- get to Geneva in time (trains every 30 min)
- TER Geneva - Lyon Part-Dieu 11:29 - 13:26
Go to the AVE platform -> look if you can spot the train whenever you arrive. Speak to staff and ask for passholder reservations.
Buy reservations in advance for the Valence - Barcelona TGV for peace of mind. If you can board the AVE get a refund for them (possible without fees until departure), if not you'll be able to use them and make it to Barcelona that day anyway :
- TER Lyon Part-Dieu - Valence 14:20 - 15:27
- TER Valence - Valence TGV 16:17 - 16:25
- TGV Valence TGV - Barcelona-Sants 16:57 - 21:27
Questions welcome. :)