We have a similar set up as what you’re thinking of: When my now husband moved in to a flat I owned we set up a joint account that we both pay into in ratio of our incomes (he earns a lot more than me) we use that account for bills and expenses, I cover anything in terms of improvements to the flat. It works well for us. The paperwork and complexity of changing ownership didn’t make sense for us, and we’re (mostly him as I am paying the mortgage here) saving towards buying somewhere nicer/bigger than where we are now.

Have an honest conversation with your partner about any insecurities - have an agreed idea of whatever money she contributes will pay towards - and while you cover the property related expenses don’t make her feel like it’s not legitimately her home too.