I think she was too hardline Catholic, in hindsight, to marry a Protestant prince, especially a non-reigning one.
OTL Duchess was off the market by 1617. OTL Countess of Soissons, however, is still on the market, provided she is willing to marry a Protestant.
If we are into ATL surviving princesses for BOTH brothers, count of Soissons had a third daughter
So WI instead of dying in 1623 at the age of 15, she becomes the Duchess of York and Kintyre the same year?
- Charlotte Anne de Bourbon (1608–1623)
Oh I i like that, Charlotte Anne it is then. That'll certainly create some interesting dynamics at court. I do wonder would Charles still go down the same high church route with a Lutheran wife at his side.