If your wife were covered by an HDHP in 2018 and did not have conflicting coverage, then she may be able to retroactively create an HSA for 2018 and contribute to it in 2019 (please, before April 15!).
It's not 100% clear to me what coverage she had throughout 2018. If she was under your HDHP with Family coverage for Jan-Mar (2018), and then immediately switched to a Self-only HDHP policy, then she would be able to contribute as if she had Family coverage for three months, then switched to Self (TurboTax will calculate the maximum contribution for you when she enters what coverage she had in which months).
However, since there is more to being an HDHP than the deductible amounts, she needs to contact the insurance carrier to confirm that her new policy is actually an HDHP policy.
In the first line, I said "may be able" because when she and you both enter you data as if she had her own 2018 HSA, the interaction of your contributions (and the excess) may cause her to be unable to contribute. However if she is 55 or older, there is a $1,000 bump for the owner of the HSA (HSAs are owned by the individual); thus, she may be able to contribute 3/12ths of the $1,000 to her HSA if she did not have have HDHP coverage after March or the whole $1,000 if she did. You'll have to enter the amounts to see what happens.
Note that to contribute to her HSA, you will want to tell TurboTax that you were responsible for the entire excess and will withdraw it. This will possibly have the effect of allowing some funding in her HSA even as your HSA has the total excess removed (if you tell TurboTax that she made part of the excess - which she actually hasn't contributed yet - she will be unable to keep anything in her HSA).
