Advice on advising niece on 1st RV purchase.

26' is fine, so is 28' and 32' unless the campsite is 24' max.

Frankly I would rather stay out of it. But I am not going to turn down her request for help.

S

Since she ASKED for your advice, I would tell her the same thing I tell everyone; Go to an RV show and see what you like and make a list out what amenities she has to have.
If she's buying used, I always suggest they avoid anything that smells like mildew (even if it isn't visible) or has had a leak. There are plenty of units out there that you don't have to deal with this headache with. Don't trust what a salesman or the nicest couple tell her about a rig. Verify everything and perhaps even hire a professional to check it out (if used).

If she's 63 years old, I think she's highly capable of making up her own mind. It's not like she's 6 years old any more. If she want's 26 feet or 46 feet, it's her call. She's the one that's going to have to live in / and / with it. Really, not much difference in 4 feet.

My thought is, what does she want to do with it? Also, will she traveling alone? Friend? Large pet? Given what you have stated, I’d suggest she also check out class B RVs.