If the OP's wife was enrolled in an HSA along with the high deductible plan she had before the marriage, she still has access to that. I have never said that she did not. However, we have not established that SHE had an HSA prior to her marriage to the OP.
The OP's question, however, related to her becoming enrolled on HIS plan so that she could access HIS HSA. Which would be perfectly fine if she were still enrolled in a high deductible plan. However, while she CAN access HER OWN HSA after switching to a low deductible plan, she cannot access her SPOUSE'S HSA while she is on a low deductible plan.
https://www.irs.gov/publications/p969#en_US_2017_publink1000204039
Right now, she is enrolled on a low deductible plan. In order to be eligible for her spouse's HSA, which is what the question relates to, she can have no coverage other than a high deductible plan. As Quincy suggested, if she wants to waive her low deductible plan since she has a qualified life event, then she will have no coverage other than the OP's High Deductible plan and she can partake in his HSA. But she cannot use her spouse's HSA while she is enrolled in a low deductible plan. If she has an existing HSA plan that SHE established while SHE was on a high deductible plan, she can utilize that; however, since there is no evidence that she does or did, I did not address that earlier.