Daughter had a bunch of huge thistles and can't get rid of them,

Thistles have a large underground root system and simply pulling them out will only cause them to regrow. I got rid of mine by spraying them with Roundup and repeating it over and over every time I saw any sort of regrowth. Took a couple of months.

Boil water and pour directly onto them

PLEASE, PLEASE do not use RoundUp; it is a known carcinogen that is toxic to the earth. I am a strong proponent of using boiling water to control noxious weeds. Pour boiling water over the lower part of the plant. Once the soil has cooled, you should be able to pull the plants with the assistance of a hand spade or hand fork. You need to stay on top of the weeds and remove them quickly before they grow too large.