Heather's match stats:

First serve percentage 61 (2013) 65 (2012)
First serve points won 64 (2013) 63 (2012) median for top 100 is 63
Second serve points won 46 (2013) 43 (2012) median is 45
First serve return points won 35.5 (2013) 37 (2012) median is 38
Second serve return points won 52 (2013) 53 (2012) median is 55

Obviously being unwell will have had an impact on the numbers for 2013, as will playing relatively few matches on clay compared to grass. What stands out to me is how poor Heather's return points won against 2nd serve are relative to other top 100 players. One way to get to use her volleys more often would be to be far more aggressive returning 2nd serve then immediately attack the net; a tactic Andy used for a spell when he was coached by Brad Gilbert.