Paddy is right. There are many threads here that answer the same or similar qiestion. Use the searh function to find them.

Some manufacturers make packs specifically for women. Granite Gear is one of them.

One caveat-if by backpacking, you mean traveling with a backpack, as opposed to hiking, I would stay away from ultralight packs-they are not made to take the abuse of being tossed around by baggage handlers, shoved into trunks or luggage compartments on buses and trains or run through airline carousels. Packs made out of Cordura will last a lot longer than silnylon.

For airline travel, get yourself a cheap, lightweight duffle bag to hold the pack-this will protect the straps from being ripped off or damages. Consider this bag to be expendable.

LL has its fans, but external frame packs are likely to get damaged in transit because the frame can easily get caught on something.