Grasso made her professional MMA debut in December 2012 in her native Mexico. During the first eighteen months of her career, she amassed an undefeated record of 5 wins and 0 losses.
After taking a year away from the sport, Grasso made her Invicta FC debut on September 6, 2014 against Ashley Cummins at. She won the fight via unanimous decision. In her second fight for the promotion, Grasso faced Alida Gray on December 5, 2014 at. She won the fight via TKO in the first round. Grasso next faced Mizuki Inoue on February 27, 2015 in the co-main event at. She won the fight by unanimous decision. The bout also earned Grasso her first Fight of the Night bonus award. Grasso was expected to challenge Livia Renata Souza for the Invicta Strawweight Title at Invicta FC 14 on 12 September 2015 but was forced to withdraw due to injury.
Ultimate Fighting Championship
On August 11, 2016, it was announced that Grasso had signed with the Ultimate Fighting Championship. She faced Heather Jo Clark on November 5, 2016 at in Mexico City, Mexico. She won the fight by unanimous decision. Grasso next faced Felice Herrig on February 4, 2017 at UFC Fight Night 104. She lost the fight by unanimous decision. On August 5, 2017, Grasso faced Randa Markos at. Grasso suffered from a UTI Infection and was medically advised to stop cutting weight and be placed on antibiotics, as a result she came in at 119 lbs, three pounds over the strawweight limit and was fined 20% of her purse that went to Markos. The bout proceeded at a catchweight. Grasso won the fight via split decision. Grasso faced Tatiana Suarez on May 19, 2018 at UFC Fight Night 129. She lost the fight via a rear-naked choke in round one. Grasso was scheduled to face Angela Hill on August 25, 2018 at UFC Fight Night 135. However, Grasso was pulled out from the bout on July 19, 2018 due to knee injury. Grasso was expected to face Marina Rodriguez on February 2, 2019 at UFC Fight Night 144. However, it was reported on December 17, 2018 that Rodriguez pulled out of the event due to a hand injury. The pair was rescheduled to UFC on ESPN 2. However, on March 22, 2019 it was reported Grasso was injured and she was replaced by Jessica Aguilar. Grasso faced Karolina Kowalkiewicz on June 8, 2019 at UFC 238. She won the fight by unanimous decision. Grasso faced Carla Esparza on September 21, 2019 at UFC on ESPN+ 17. She lost the fight by majority decision. This fight earn her the Fight of the Night award. Grasso was scheduled to face Cláudia Gadelha on January 18, 2020 at UFC 246. However, on the day of the weigh-ins, Grasso weighed in at 121.5, 5.5 pounds over the non-title strawweight limit of 116 lbs. The NSAC decided to remove the fight because competitors are not allowed to compete if the weight between them is over 3 pounds. In a statement released just hours after the weigh-ins, Grasso apologized for missing weight, and declared she will now be fighting at flyweight.
