FYI, both my bikes are a 9 spd ultegra/XT mix by choice. I have no problem finding 9 spd replacement parts. I chose 9 spd so I can mix road and mountain parts, to let me use a compact double in front, with mountain gearing in back for mountains. Heck, you can still find 5 spd parts. Try someone like Harris Cyclery.
You are also ignoring a critical fit factor by focussing only on top tube length and not seat tube angle, both of which effect reach.
This is how the seat tube angle stuff works. All you have to understand is that every 1 degree increase in seat tube angle pushes the seat tube closer to the bars, so while this can be used to reduce the top tube length, it doesn't change the reach, because the saddle then needs to go back 1 cm to get the same KOP position. So in other words, the REACH ON the following bikes are identical:
BIKE STA TT
1 73 52
2 74 51
3 75 50
4 76 49
The problem is that someone might purchase bike 4, thinking it has the shortest top tube, without realizing that it is identical to the other choices. For ME, the problem with too steep a seat tube is that even with the saddle all the way back on the rails, my knee is too far forward of the pedal axle. So, as she test rides bikes, note both the seat tube angle and top tube length (assuming she has adequate clearance over the top tube and can get the bars to the desired height easily). Once you know her ideal geometry, its easier to shop around on ebay. I got a never been built terry isis frame that sold new as a complete bike for $2000 for only $100 on ebay, and then just swapped all the relatively new parts from an older rusting bike to make a helluva sweet ride. This doesn't have to be expensive, but you do need to know what frame geometry you are looking for.