It's very difficult at most schools to get a bid if you're a senior, unless you're on a 5-year plan. You will only have one year to devote to your chapter and bond with your chapter sisters.
At some schools, juniors and seniors are "free" (not counted in quota) so that a bid offered to an upperclasswoman doesn't mean that an interested freshman or sophomore goes bidless.
There's no harm in rushing. After all, if you don't rush, you definitely won't be in a house.
Good luck!
