The Powerglide was used in the passenger cars, not trucks. It was an extremely heavy cast iron 2-speed, "too-low" and "too-high" on the gear ratios! Not a good choice for a daily driver! I respectfully disagree with your advisor about the TH-350- - - -it's a very rugged and reliable transmission without all the throttle pressure adjustment issues of the TH-700/RL-60 transmissions. The 700 does have overdrive, which makes the stock 3.90:1 rear end a little more highway-friendly. Unless your girl plans to do a lot of highway-speed driving, I'd reccomend going with the 350 trans.
Jerry