Marrying a Non EU citizen who is in UK on a family residence Card

[ArtizanUK]

I hope someone can point me in the right direction of what I need if anything. I am engaged to a woman who is in the UK on a family EU shengen family residence visa and has a UK residence card.
She is from the Cameroon and is living here in the UK with her daughter and her husband who is polish. She current has a residence card as a family member.
We want to get married and live here in the UK with me (a UK National) Can we just get married or do we need to go through the visa process again for a marriage visa before we can do this?
With all the brexit stuff going on, and the fact that her residence is through an EU Family residence, as her son-in-law is polish, I don't know how and if this will affect us

[CR001]

In order to marry in the UK, you and her have to attend an HO approved Registry office to give 28 days notice. The registry office then inform Home Office and this notice period can be extended to 70 days for HO to investigate and/or interview each of you separately to rule out sham marriage or marriage of convenience. Only once you get HO approval AND you are both free to marry, then can you then marry.

She could then once married to you, apply for a UK spouse visa if you/she meets the requirements (English A1 test, financial requirement, adequate accommodation) and it costs £1033 visa fee plus £1000 Immigration Health surcharge for the first 2.5 year visa.