So... That's an interesting result of a battle.
I was thinking, does the Alliance has any noticable ship reserves?
And if they were loosing severily, would they ask someone (maybe Colonial union...) for help?
The Alliance was caught off-guard by a larger than expected Lothari fleet. They thought they had them beat. The Lothari tech advantage, particularly the anti-fighter missiles, really helped them a lot, and about two thirds of the Alliance fleet were older designs that hadn't been refitted. That hurt, a lot.
The Alliance is vast, compared to the Kingdom of Lothar, so this defeat shouldn't be fatal. Or even a big deal in the larger scheme of things. While the Alliance doesn't have much of a mothball reserve, their total navy is much larger than that of the Lothari, its merely a question of how much they feel they can strip from other areas of the Alliance without exposing themselves too much. Indeed, heavy reinforcements are almost at the front lines, and thus will be able to make up the losses fairly quickly.
On the other hand, the Lothari have a large mothball reserve, which they have been steadily reactivating. This is where a good portion of the ships that surprised the Alliance fleet came from. Still, their resources are limited compared to the Alliance, which has an income many times that of the Lothari.
If they need help, the Alliance will first turn to their associate members. They have three associate members that are relatively powerful, the Torqual, the Doraz, and the Zir. Unfortunately, none of them have fielded fighters yet. Also, the Doraz are focused on the Aurarii, and suffered heavy casualties during the war. The Torqual remain relatively powerful, and have a moderately large fleet, but are also focused on the Aurarii and would need time to re-deploy against the Lothari. And the Zir are, well, the Zir. They are pacifists that believe in a strong defense and have declined to send ships to aid the Alliance at this time. The Alliance has allowed this to happen without comment because Zir territory is under threat from the Mintek and having the Zir fleet at home helps the entire Alliance. The Alliance's various other associate members are too small and too low-tech to really contribute anything significant.
After the associate members, the Alliance could in theory turn to the Colonial Union or the Confederated Sentient Races. However, it is unlikely to do so except in the most extreme circumstances. After all, they just fought a border war with the Colonial Union that was entirely their fault, so the CU would be unlikely to help. And the Confeds have been deeply distrustful of the Alliance from the start, which is understandable given the manner of their first encounters. The two members of the CSR, the humans and the Bjering, met the Alliance after two of its founding races launched an unprovoked invasion of human space, with the Rehorish actually violating a defense treaty it had with the human states to do so. The Confeds have a trade relationship with the Alliance but are unlikely in the extreme to form a closer relationship.