My 4 yr old has a bottom loose tooth, she is healthy. Is that to early to lose a tooth?

A little. Some can begin losing their baby teeth quite early 4yrs is not unheard of.
Loose tooth. The lower front baby teeth usually get loose and fall out between the ages of 5 to 6. Some children get their baby teeth early, some late. The permanent teeth can also be on their own schedule. The sequence of which teeth fall out is more important. If your child fell or hit her tooth, they may loosen and tighten up on their own.
It's early but. The date range to start loosing teeth is just a range. It is not a set in stone law. Some are earlier and some are later. If the tooth is not decayed, painful, or has swollen gums around it. Likely it is exfoliating properly. If concerned definitely go see your dentist especially if it has been awhile.