Harmony might actually be good preparation for Serena. She likes to drop shot her opponents to hell after pushing them to the back of the court, lots of net play is on schedule so it will be interesting to see if Serena's vertical movement (mostly) will be up for the job.
Having seen Serena play two doubles matches, I think Serena's serve will be too much for Harmony, though I did see that Harmony reached the semis of Gaibledon (losing to AVU) so at least she has some grass wins under her belt.
Serena's form is doubtful still at the moment. She just played like 2 doubles match at 40 and after 1 year not playing competitively. If Serena is moving OK and has stamina still (can last more than half an hour) , should be no issue for her.