Part of the decision depends on what she leans toward musically. If she specifically wants to play piano, then lean towards something with "hammer-action" and 88 keys, which is going to be more expensive for something with decent quality. If she leans more toward a mix of piano/organ/electric piano/synthesizer, then something with synth-action or semi-weighted keys will be a good choice.
I play the mix noted above. My preference is 76 synth/semi-weighted keys. I don't like hammer-action keys for organ/synthesizer. 61 keys is a little limited. It's hard to find synth action in an 88 key board, so 76 unweighted keys is the sweet spot for me. I have a 61 key Yamaha, a 76 key Casio, and an 88 key Casio digital piano (in addition to still having the accordion my parents bought new for me in 1973, lol), so I have most of the bases covered.
Make sure you get something with velocity sensitive keys. i.e. if you hit the key harder (faster) it's louder, softer (slower) it's quieter. Something without velocity sensitive keys is closer to a toy than a true musical instrument for learning and will probably discourage her due to the lack of dynamics.
Also, make sure you get a good quality board like something you'll find on Sweetwater (Roland, Yamaha, Korg, Casio, etc.) vs. the generic stuff you might find on Amazon or eBay. Jeremy See's recommendations are probably a good guide. Also, spring for the AC adapter if the board doesn't come with one. You can burn through batteries pretty quickly.
I started off on organ when I was young and then my parents put me in accordion lessons (cringe!). Playing on a real piano or a digital piano has never been a problem for me.