Hi,
I have to use a wheelchair for long distances also...like going to the mall (and the zoo!

) and such...I get tired pretty easily when walking, but I always used my walker to get around in school, I just took breaks when I got tired, left a couple minutes earlier for class, etc. .... everything worked out fine in terms of walking, I guess it just depends on how much muscle strength your daughter has and whether she prefers using the walker or wheelchair.
As for how the other kids will treat her, I honestly can't tell you 100% what to expect, but as for me....well, every kid gets picked on to some extent growing up--kids are cruel sometimes--but I never experienced anything too bad at all. For me, I got more insecure as I got older (probably because of the whole "dating" aspect), but at your daughter's age it seems that most kids may question why you are "different", but you can give them an answer, they say "oh, ok", and then they forget about it and treat you like everyone else.
If she is going to be going to places like stores and things in her wheelchair, the only thing I would tell you to prepare your daughter for is people staring, as well as young kids who often point and say "Look at that!" and such....just let her know that some people may not be used to seeing a wheelchair, but that doesn't mean she should be embarassed...people are just curious, but just smile and say hi