updated 08/05/2016 AT 05:20 PM EDT  •originally published 08/02/2016 AT 07:00 PM EDT  has a special friend looking after her.  Before she was diagnosed with breast cancer, the former  star says her dog, Bowie, was actually first to detect something was wrong.  "She would obsessively sniff right here on my right side for a long time before," Doherty says in a preview of Tuesday's episode of  . "So, it made sense when I got diagnosed."  last August that she had been battling breast cancer since March 2015.  to the lymph nodes, and from one of my surgeries we discovered that some of the cancer cells might have actually gone out of the lymph nodes," Doherty said during the  interview. "So for that reason, we are doing chemo, and then after chemo, I'll do radiation."  In May, the actress underwent a single mastectomy describing the entire process as "traumatic and horrible." However, her beloved dog was still by her side.  "When I got back from surgery, [Bowie] again was kind of right in this area," she says, gesturing towards her right side. "Then when I had my first chemo, she would sniff my entire body up and down. And she was always protective before, but she has become this crazy, protective dog. It's hard to get close to me when she's around."  On Friday, Doherty shared a sweet Instagram snap of "Ms. Bowie" laying next to her in bed and opened up about her chemo struggles to her followers.  "Each persons cancer journey is different. For me, chemo has been terrible and believe me, we have tried almost everything. So days like this have become a bit of the norm. I'm learning that it's ok to fall into bed and give in to the exhaustion or nausea or aches," Doherty penned. "I've learned a lot of that thru all the beautiful people who have shared their personal stories with me right here on Instagram."  "Btw, it doesn't hurt to have #msbowie comfort me So back to my nap," the captioned continued before she thanked her supporters. "Thank you for your prayers, well wishes and stories. They help so much."  Though Doherty continues to fight for her life, it comforts her to know that her cancer has in fact strengthened her marriage to  "My marriage was always strong, but it's made my marriage a thousand times stronger," she says in the preview. "I could not have gotten through this without my husband."
The former Beverly Hills, 90210 star says her beloved pet gave her warning signs before her cancer diagnosis