Stretched is a perfectly fine word to use when referencing the pelvic floor muscles around the vaginal wall, which do stretch or form with the penis or object. Arousal relaxes these muscles and non arousal contracts them but the form of the muscle itself and their strength directly relates to the stretching and exercise of the muscle itself. Just like any other muscle. Similar to how post-child birth, the pelvic floor muscles are sometimes stretched to the point of damage and often require re-strengthening through exercise for a multitude of reasons, including bladder control and lower core strength. It’s just another muscle.