The overwhelming majority of Petra's losses last year (whether healthy, sick, injured, etc.) were against top top 10, 20, 40 players.
The two worst losses she had (if you go by Pervak's ranking), where against Hredecka and Venus Williams. Lucie H. was ranked 105 and and Venus 134.
Comparatively speaking to Pervak (besides Petra dealing with playing against her friend and teammate--Lucie H., and battling the Miami Asthma against Venus): These two can hit any body off the court on a good day (especially if you're not playing well). No embarrassment there, in that respect.
Caro's situation is totally different. She's getting hit of the court by players with little to no offense, regardless of their ranking, when she's completely healthy (unlike Petra last year, who's worst losses to higher ranked opponents--mind you, coincided with various illnesses).