I need a strong saber to fight against altria in camelot

Well, your options are limited. The only ST Buster Sabers in EN right now are Brave Elly, Rama, and Bedivere. The first is event locked, the second is 4* gacha with no rate up, and the last isn't even possible to have until after Camelot is complete; without friend support, NPC Bedivere is probably the "intended" way to win.

Yu could try Okita Saber as well, but she's Quick, so less damage. Other options would be the ST Buster Berserkers, but they have issues living.

I used my maxed Brave Elly (because I <3 Elly), and buffed her with Lancer Elly, Ceasar (Order Change), and support Zhuge to charge and buff Brave Elly at the same time, with maxed Holy Night Supper CE on her.

Beat final Laltria in four turns, with 2/3 of her HP taken out on the first turn.

Saberlot (lancelot) will be good as well.
i used hercules, altria and support waver. when herc is dead.. lancelot & mash saves the day. All 3 are lvl 90 but their skills are not maxed as i'm kinda poor on materials BUT you will need mash to soak some damage.

What sabers do you have, or are you looking to borrow one?

Actually Artoria OG, Waver and Mash(max skill) is enough to fight her.. I kill her with this team in 6 turn. Rhongomyniad not hurting at all when buff from Lord Camelot + Mash def buff + waver def buff is active

You dont really need fancy saber to fight her just strong defensive support like mash and waver i beat her with just fergus and caesar the key is you need to pop mash wall of snowflake and waver damage cut before she use her np

I borrowed a friend's Mordred because she is made for that fight for memes lol. But hey, it actually worked with my Strat.

Also, that fight is one of the rare moments pre-rank up Sumanai works like a charm. Artoria is a Lancer AND Dragon there.