Not inviting step-parent to wedding

Ok so.
My fiancé’s mother passed away about a month before we started seeing each other 3 years ago. Although she isn’t physically present we very much want to include her in our wedding (memorial table or something of the sort). This included originally keeping her spot free at the top table so it is clear somebody is missing.

About a year and a half into our relationship, future FIL started seeing someone. I wasn’t overly keen on her (can’t put my finger on why, but I didn’t trust that she wasn’t even divorced at the time they started seeing each other) but was pleased he was so happy. They announced their engagement approx. 6 months before we did.
Then about 3 months after fiancé and I got engaged, she was INCREDIBLY rude to me at a time when I was really struggling with my MH (longtime anxiety and depression). There has been no apology and I havent seen her for at least 6 months now (a combo of lockdown and avoidance on my part as she now is a major anxiety trigger).
Fiancé and I are having a pagan handfasting next month with close family and friends. We have invited his dad who has said he won’t come unless she is invited. It is really important to me that there is no negative energy at the handfasting so I have said if she sincerely apologises she can come. I’ve since heard nothing.
I know it means a lot to my partner to have his dad at the handfasting and also at our legal church wedding and reception next year, but I just really don’t want her there to possibly ruin the day with her immature behaviour. Fiancé understands how I feel but is feeling torn between hurting my feelings and hurting his dad’s. My opinion is that if his dad cares enough he will come to both regardless of whether she is invited.
Our reception is £80 a head and if we invite her we will have to invite her children too which will add up to around £400!
Any advice?