What have you got on now is it a shimano?
Ask him if if he means the bit which the pedals attach to or the bit at the back of the bike on the rear wheelYes but it's a racing block and I struggle to get up some hills and is putting me off cycling a bit
Suspect that with him mentioning compact, she probably has a standard double and with racing block being mentioned probably a 11-23 or similar. The cheapest solution is just to change the rear cassette to something like 12-30 , that will get you up pretty much anything even if it is a double up front.
http://www.cyclechat.net/threads/shimano-ht-ii-chainset.148507/
Do you mean 50-34 rather than 50-43?
Yes think so now after checking loads online
Except that 172.5 mm cranks are on the long side for most women?