Maybe she's painted it invisible? The craptastic Google Translated tags (箒が混じってないといいね + 血のにじむような努力の結晶) make me think she's cleaning up/painting over a nosebleed, perhaps?
It's a pun on 毛編み, which means "knit", but is literally "hair-woven". In the first panel, you think she means （魔理沙の）（毛編みマフラー）, "Marisa's knit muffler", but in the fourth panel, she breaks out the lint roller and you realize that she means （魔理沙の毛）（編みマフラー）, "a muffler knit out of Marisa's hair".
Oh! So its not a paint roller, but one of those hair-cleaning rollers! She rolled up the excess hair Marisa lost and after doing it for who knows how long she made a muffler out of it. Wow... that's dedication! I can't imagine how long it would take to get enough hair for that unless Marisa sheds like a dog!
It's finally complete...Girl is reminiscing...Marisa's handmade muffler...*roll roll*
