Hi, Candy (that's my sister/buddy rider's name!) I echo everything R. M. said but 1 1/2 hrs is enough time to get from F gates to G gates (IF your flt is on time)
Personally, I would fly DTW to LHR--you will very likely get biz elite (0 nonrevs listed for 11 seats) You'd have to leave Den AM or connect thru MSP (a few options). You can get a cheap day rate hotel in Romulus or buy SkyClub pass for $39 (I think) . The 4:19 flight DEN to DTW is pretty tight but both usually use A Gates. Gotta say ATL looks better for biz than MSP (if no upgrades show up) Nice seniority on your pass. Thank your employee profusely! Good luck. Come back and let us know how it all went, ok?