It depends a bit on your appetite for changes and how much you care about the journey time and cost. Given that you want flexibility for the return journey, the best option in terms of tickets is probably just to buy flexible walk-up returns.
Least changes - CrossCountry
If you want to minimise changes as much as possible (e.g. if you have a lots of bags) you could take CrossCountry to Reading and change there for an Elizabeth line service to Hayes & Harlington (HAY). It's not the fastest route but it involves just one change. If it were me, this is probably the option I'd go for.
You'd buy a Wolverhampton (WVH) to HAY Off-Peak Return (SVR), route "not via London" for yourself (£51.20) and an equivalent SVR from Coventry (COV) for your wife (£47.00). The only wrinkle is that you would have to buy these at a ticket office or ticket machine, since online retailers won't sell Two Together discounted tickets for one passenger - in this case, your wife's season ticket covers the journey as far as COV hence she only needs to buy a ticket from there, which is a bit of an 'edge case'.
Getting to the hotel
From HAY you could either continue on the Elizabeth line one/two stops to the relevant Heathrow Terminal (£5.15 each for an Anytime Day Single or £9.85 for an Anytime Return), or take a bus directly to your hotel (£1.75 each with contactless). If your hotel is on the north side of Heathrow (e.g. the Bath Road) then the bus from HAY will probably be just as quick, not to mention much cheaper. That would make the total something between £108.50 and £117.90.
Cheaper - WMT or Chiltern
If you want a cheaper option, you could take West Midlands Trains (WMT) to Euston (EUS) or Chiltern Railways to Marylebone (MYB). However, both are fairly slow options, and require one or two changes at Smethwick/Birmingham/Rugby just to get to EUS/MYB - let alone HAY/Heathrow. From EUS, the best way onwards is taking the Northern line (Charing Cross branch) to Tottenham Court Road and then the Elizabeth line. From MYB you'd take the Bakerloo line to Paddington and change onto the Elizabeth line there.
WMT don't offer through fares to Heathrow or HAY; therefore, if you're taking the train to Heathrow you'd be best off buying a Super Off-Peak Return (OPR) to London Underground Zone 1 (£26.30 each - the fare is the same from COV) and then an Anytime Return from Paddington to Heathrow (£16.35 each). If you're taking the bus from HAY then you would be better off buying the OPR to EUS (£22.30) and using contactless from EUS to HAY, costing £3.60 each. The total cost would thus be between £72.80 and £85.30.
Chiltern do offer through fares to HAY routed "via High Wycombe", so you'd be best off buying an OPR to HAY (£34.80 - again same fare from COV) and then singles to/from Heathrow as necessary. The total cost would thus be between £79.90 and £89.30.
Faster - Avanti
The fastest option would be taking Avanti West Coast to EUS and then as described above. Avanti run one direct train an hour from WVH, which in most hours runs non-stop after COV; though you can also change at Birmingham if you prefer. They offer "via London" fares valid on any operator; such an SVR from WVH to HAY would be £54.25, and £48.85 for your wife from COV - again, add singles to/from Heathrow as necessary. Total cost thus between £113.40 and £122.80.
