Brianna MacKinnon’s been pulling 12-hour shifts at the factory where she works in Springfield so she didn’t get home until late Wednesday night.

“My Facebook page was all lit up,’’ she said. “I couldn’t believe what I was seeing.’’

What she was seeing was friends of hers, fellow veterans, being told that because they were transgender they could not serve in the US military. President Trump’s tweet not only purported to ban transgender people from serving, it insulted the service of veterans like MacKinnon.

“Outrageous,’’ MacKinnon said. “I’m really angry. In polite company, I can’t tell you what I really think.’’

She grew up looking up, to her dad, a Vietnam War combat veteran. But even as a teenager, she felt like a girl, not the boy everybody knew her as.

“I joined the Army to prove I was a man, and then I realized I was not,’’ she says.

But that realization had nothing to do with her ability as a soldier. Between active duty and the reserves, she gave the Army 23 years of service. During Operation Desert Storm, she was a field artillery surveyor, meaning she helped keep other soldiers alive. She went from Saudi Arabia to Kuwait and served honorably. In the reserves, she served as an artillery drill sergeant.

When she served, “Don’t Ask Don’t Tell’’ was the law of the land and if gay soldiers kept a low profile, transgender soldiers stayed even lower.

“But the reality is that transgender people have been serving from the beginning of the Republic,’’ she said.

MacKinnon began transitioning in December of 2014. Her fellow veterans at the Earl J. Sanders VFW Post 754 in Amherst could not be more supportive.

“Bri served her country honorably,’’ said Victor Nunez Ortiz, a Marine veteran and one of the post’s leaders.

Last April, MacKinnon was elected the post’s junior vice commander and adjutant. She serves on the state VFW color guard.

Oh, and by the way, Bri MacKinnon voted for the guy who wants to ban transgender people from military service.

“I voted for Trump, but that doesn’t mean I support everything he says,’’ she said.

She believed Trump when, in the middle of the campaign, he promised to support the LGBT community. When Trump said he’d do more for LGBT people than Hillary Clinton, Bri MacKinnon believed him.

“I’m a Republican,’’ she said. “I voted for Trump because I haven’t liked the Democratic Party since the Vietnam War.’’

She finds history fickle.

“Back in the 60s, the Democrats in the South were against the Civil Rights Act,’’ she said. “Now it’s flipped on LGBT rights. My party is against them. I have to fight them to change that.’’

Her voting for Trump did not make her popular with other transgender veterans.

“Before the election, I was called a quisling by several transgender sisters,’’ she said.

Now, a president who did everything to avoid military service, a president she voted for, has decreed that she and any transgender people should not serve in the military.

She thinks Trump’s claim that transgender soldiers, airmen, sailors, and Marines hurt unit cohesion is specious.

“It didn’t affect unit cohesion when gay people were allowed to serve openly,’’ she said. “It didn’t affect unit cohesion when black people were integrated into the military. Unit cohesion has not, will not suffer with transgender people either. Soldiers are soldiers.’’

She doesn’t buy Trump’s claim that paying for transitioning treatment will cost the military too much.

“Please,’’ she said. “They’ll spend more on Viagra. You’re talking about an infinitesimal part of the military budget. Please.’’

Bri MacKinnon is 56 years old, a conservative in the ultra liberal Happy Valley of Western Massachusetts, a proud military veteran and patriot whose service to her country, whose very being, has been denigrated by the guy she voted for president.

She stood in the middle of Post 754 Thursday night, tired, angry, confused, and more than a little hurt.

Kevin Cullen is a Globe columnist. He can be reached at cullen@globe.com.