This form is the larger and stronger one, with a high damage output but a relatively slow attack rate. Her bite attack may look like it has a specified range because of the formed gap between her head and body, but targets a wider area. Still, treat her like most other enemy units with this kind of area of effect.
The snake form may be bulky in health and an annoyance for her powerful bite attack, but the fight should not be difficult as long as you do not get out-stalled. Just stack up on long range-attack cats like Dragon Cat and at least one heavy hitter such as Bahamut Cat. As long as they can outrange this form of Charlotte, all you need to do is protect them by spamming other smaller cats. The doll form, on the other hand, should be an easy kill and not require any particular strategies.