Can I enter my S/O's 1098 form if I'm not on it or on the title? Even if the mortgage was deducted from her bank account? I'm claiming her as a dependent this year.

Probably not.

From IRS Publication 936:

    You can’t deduct home mortgage interest unless 

• https://www.irs.gov/publications/p936#en_US_2022_publink1000229915

although this doesn't help you Pub 936 also says "If you're married and file a joint return, your qualified home(s) can be owned either jointly or by only one spouse."

This article discusses possible ways around the lack of ownership, including something called "equitable ownership"  or changing legal title (for future years). This is very unusual and it probably doesn't apply to you (based on what you've said). If it might apply, you should seek professional advice from a CPA, tax attorney, or Enrolled Agent.

• https://www.linkedin.com/pulse/deducting-mortgage-interest-when-your-name-deed-daniel-morris/?trk=pulse-article_more-articles_related-content-card

Also the Form 1098 instructions say "Each borrower is entitled to deduct only the amount each borrower paid ..." So if you are not a borrower or didn't pay that implies that you cannot deduct. (Instructions are not law and there could be an exception like for married taxpayers.)

• https://www.irs.gov/pub/irs-pdf/f1098.pdf

Perhaps someone else can comment upon whether the dependency relationship matters here. I don't see how. 

I will also note that unless your itemized deductions are more than $12,950 (2022 single filers), deducting mortgage interest (or taxes) won't matter. Itemized deductions include mortgage interest, state local income and property taxes (max $10k), charitable contributions and some others. Since you get the vey large standard deduction since 2017, very few people itemize (< 15%).