I didn't read everyone's advice.
I didn't need to to throw my vote in.
I would upgrade the body before anymore lenses.
Just the t5i would be a good leap. The new 7D II would be an ever bigger leap.
Like the jeweler we husbands go visit this time of year, they indirectly ask you to put a value on your love. Maybe it's time she had a 5D III and a nice 24-70mm f/2.8 II. She will be set and so will you (for a while)
takesome1, good point about the jeweler. If only wives visited the camera store the same way husbands visited the jeweler!
As for the 7D2 or 5D3... while we all love those cameras, the Rebels and xxD bodies are designed for the entry-mid level consumer shooter. The (much) higher cost and feature sets of the D series bodies might be wasted if those superior features aren't needed, valued or even understood.
And how much better does a 1 ct perform than a 1/2 ct diamond?
But you speak the truth. The best thing the OP could do is casually drop a few questions. Ask if she thinks Full Frame cameras are better, what they do better and why people own them. If she is kind of clueless he could hang with the crop bodies. If it looks like she wouldn't benefit from Full Frame I would watch and see if she is still using the icon's for shooting like the running man, portrait head, mountain for landscape. If so the t5i is probably enough camera.
If she hasn't learned to shoot in manual mode I would probably stick with the t5i. She would probably be very happy with it and a new lens.
My wife has a t5i, I just bought a 7D II. I own a 1D IV and a 5D II. She kind of understands the running man, portrait and mountain icons. I wouldn't give her the 7D II, for what she does the 7D II without those icons and the flip screen it wouldn't be as useful to her. I let her use the others sometimes but the pictures are usually a mess.