Unfortunately we usually only hear about these things when they go wrong (except for the comment in this thread by MrSelfDestruct).
I've seen plenty of other ladies who, just like I do, require deposits for overnights, weekends, evening appointments. Looks like this woman is asking for a deposit for outcalls. I personally require the same, which for me is usually $50 unless it's a significantly far/difficult drive... which is what, 10-15% of my total outcall rate. I don't think that's unreasonable; if you don't want to put down the deposit then the solution is simple: incall.
Speaking for myself, I require the outcall deposit because I've been sent on one too many wild goose chases. The last outcall I did before requiring a deposit, I show up & the guy tries to tell me that he'd misplaced his wallet & only just realized it which I could tell was BS. He wanted me to trade for a $30 bottle of whiskey that he tried to convince me was worth a lot more. He's like, oh you can go get a store credit at BevMo. Oh wait, you don't drink? Well you can give it to someone as a gift!
That was after multiple outcalls to fake addresses, and experiences like receiving counterfeit bills, being shorted, and "let's meet first for coffee"'s that were a complete waste of my time. So now I require a small deposit LOL.
I'd just suggest: don't give a deposit for someone who doesn't have a substantial review history & someone who doesn't have an established reputation as 'one of the good ones'... if you have to spend any time worrying whether or not she's going to make good, then you probably shouldn't do it.