My sister had red marks on her face treated with liquid nitrogen (sun damage), the marks swelled up quite a lot after the treatment, even gave her a 'bag' under one eye for a little while, and it all looked really sore. Will the marks turn black like scabs and fall off (ugh) and if so, how long does this take? She is treating with warm salt water and sometimes a little vaseline. she wants to look OK for christmas if possible!