Have you met her in person?
If you want to marry in the UK, you apply for a 6 months fiance visa, which costs £1523 and you must marry within the 6 months. She needs to meet there English requirment with a test form a ukvi approved test centre and you need to meet the finaicla requirment if £18,600pa. A fiance visa won't permit her to work or use the free NHS service.
Once married and before her fiance visa expires, she applies for a spouse visa on from FLR M. Cost is £1033 visa fee plus £1560 immigration health surcharge. The visa will be granted for 2.5 years.
Before the spouse visa expires, she applies for another 2.5 year visa extension, paying the same visa and immigration health surcharge fees again.
Once she has almost 5 years kn the spouse visa, she can apply for indefinite leave to remain, which currently costs £2389 and share needs a higher level of English test and the Life in the UK test.
For each stage you must show evidence of meeting the financial requirements and subsisting relationship.
Visa fees increase every year in April.
For each step she also need to enroll her biomterics.
https://www.gov.uk/uk-family-visa