she may have been entitled to file as HOH

a married taxpayer who is a US citizen or resident can file as HOH IRC sec 7703(b) if all the following tests are met

1) she files her own return

2) she paid more than 1/2 the cost of keeping up their home for the year

3) she lived apart from you for the last 6 months of 2019

4) her home was the main home for more than half the year of her child, stepchild, adopted child or foster child. the child must be a dependent or would be a dependent except that she released the exemption to you - the noncustodial parent

then all you can do is file as single

if there's a failed test all you can do is file as married filing separate - you can not force her to file a joint return.  note if she itemized so must you or if she took standard so must you.