Personally it depends on the use case. If you're mostly going to play at home or docked; the standard switch is the way to go, plus it has a better battery life.
The lite however is cheaper, and a bit smaller, so ideal if you're essentially going to treat it as a gameboy - it CANNOT be docked though, even if you bought a dock later; the controller sides are fixed so can't be replaced/changed out, and some games REQUIRE joycons so you may find yourself having to buy more (and they're not cheap).
The Pro controller is absolutely wonderful if a bit pricey; comes up for around 45 on sale but its not cheap. Me and the wife absolutely love both of ours though.
There is also the possibility there will be a revised 'Pro' switch around Christmas; its heavily rumoured so in your case, maybe better to buy the Lite (it can be had for around £170 new if you get lucky or around 195-200 with a game); and then pickup the full version come Christmas/next year if it gets used and a Pro dockable version arrives. The original Tegra chip used in the Switch V1/Lite/V2 I believe have been discontinued now so Nintendo will have to launch a revision of some kind.
Personally I love the machine, but it's not perfect, plus its noticeably weaker hardware wise than the others now, so if she cares about that, factor it onboard.