Hello PetenClaire,
When you're ready to make a visa application as fiancee you must complete this online.
As a guide its often helpful to download and print the application forms so as to get a better idea of the specific questions that need to be answered and the documents that will be needed.
The forms you'll need are:-
VAF4A - Family Settlement Application Form
Appendix 2 - Financial Requirement Form
If the father of your daughter is a British Citizen then your daughter will most likely be eligible for a British Passport and as such will not require a visa. In this case you should both prepare to apply for a British Passport for her.