Donna Allison was not satisfied with an assurance from the Manchester-based firm via its Twitter account that only fake fur is used in the products it sells.
The shoes, which were sold both online and at its Westfield Stratford store in east London, list only man-made materials on the label. However, laboratory tests confirmed that the pompoms were made from cat fur.
Allison said: "I find it horrifying that Missguided and other retailers are selling real fur."
The import and sale of fur from domestic cats and dogs has been banned across the EU since 2009. Details of the Missguided shoes have been passed to trading standards for investigation. In further laboratory tests, another pair of shoes from Missguided tested positive for rabbit fur.
A pair of gloves at "fur free" retailer House of Fraser tested positive for rabbit. A range of shoes sold by the firm Parmars at a store in Westfield Stratford, which were sold as using fake fur, actually contained rabbit, mink and fox.
A bobble hat sold on Amazon UK as faux fur tested positive for raccoon dog, despite the fact that the listing included an on-screen no-fur assurance.
Another bobble hat sold on fashion boutique website Lily Lulu as "faux fur" was labelled as 10 per cent marmot on delivery. It subsequently tested positive for raccoon dog.
Selling products from cat, dog and seal fur is illegal in the UK and across the EU. However, imports of fur from a range of other species such as fox, rabbit, mink, coyote, raccoon dog and chinchilla are allowed.
Claire Bass, of HSI, said: "We know the vast majority of British people reject the inherent cruelty of the fur trade but they are not getting the right information as consumers to avoid it."
Missguided stressed that it had a strict no fur policy and removed the shoes from sale after being informed of the findings.
House of Fraser has stopped selling a pair of gloves identified as having rabbit fur trim. It said: "We have a strict no fur policy and ensure all of our suppliers and brand partners are aware of this.
"We would never knowingly mislead our customers. We are extremely concerned that fur can be mislabelled in this way."