I'd think about the role as a role. Is there a job description? If so, what are the specific responsibilities. What would you pay for the role - comp it to market and company hiring practices. Then, determine if you need the role. Then, open the req and recruit for the role / encourage her to apply. Then, put her through the same interview process as everyone else.

You have to treat your business as a business. If you need the role, are paying a fair rate (salary, bonus, equity) and she's the best candidate, hire her. Then, you have a process that you can be transparent about and is fair.

Don't be bullied into something like this - it could be the beginning of the end.