There is no employment or income requirement for making an HSA contribution. Since your spouse is covered by your HDHP plan through your employer, she can make a contribution to her own HSA.
The $6,750 contribution limit for having family HDHP coverage will be split between the two of you, so unless she was age 55 or older during the tax year and therefore can make a catch-up contribution for herself, you won't be able to increase the combined amount contributed to HSAs. If she was age 55 or older in the tax year, she can also make a $1,000 catch-up contribution (or some fraction thereof if you are not eligible for an entire year's contribution) to her own HSA.
