POD her OTL death in January 1594. She was a bit over 1 year old (born sometime in 1592), no special reason to assume she was especially frail - just a random childhood illness, and if butterflies just avoid it, she can grow up a child as healthy as any other in her time.
And the natural illnesses of her father Czar Fyodor, her mother Czarina Irina and her uncle Boris go just per OTL schedule. Also, her parents´ subfertility takes the same natural course - as per OTL Irina bears no further children 1594...1598, neither sons nor daughters.
Recapitulate the family relationships:
Vladimir of Staritsa and most his children had been killed in 1569;
his only surviving child was daughter Maria, by 1598 a nun incarcerated in Russia and 38 years old, with both her children dead;
the House of Moscow had been exterminating cadets for some time, so the Ryurikid cadets left alive were very distant and also lacking in wealth and connections.
This is why OTL, Boris Godunov with no Ryurikid descent was made Czar without an immediate civil war, and Irina was alleged to have been seriously considered.
Now, minority was in principle accepted for the throne of Moscow. Ivan the Terrible had acceded, age 3, without fight even though he had a couple of middle-aged bachelor uncles available. But there appear to have been some hesitation: when Ivan Terrible fell seriously ill in 1552 or 1553 (the story is not exactly dated), he wanted to be succeeded by his baby son Dmitry (who lived to 8 months, so the age limits are under 8 months and possibly under 2), many boyars expressed reluctance (somehow in the face of the sick Czar, instead of swearing and then breaking the oath when Ivan was safely dead), wanting the succession of Ivan´s cousin the said Vladimir of Staritsa (then 19...20).
So. In January 1598, Fyodor dies as per OTL. Recapitulating the obvious family:
on the male line, Fyodor´s little brother, Dmitry, as been dead for nearly 7 years, and would be 15 if alive. And did not OTL reappear for the next 6 years
the mentioned Maria of Staritsa, a nun of 38
a bunch of very distant and unimportant Ryurikovich princes;
through marriage, Czar´s widow Irina, about 40 years old
Czarina´s brother, Konyushi and de facto established regent for over 10 years, Boris Godunov, age 46, with a healthy son Fyodor, age 8;
influential but decidedly subordinate boyar Filaret Romanov;
a bunch of other boyars like Vasily Shuiski.
All as per OTL.
And the major difference - a 5 year old apparently healthy daughter of the late Czar.
Considering the above described poor alternatives: would Moscow of January 1598 acknowledge a 5 year old girl as their Autocratrix?
And how about regency? For formal regent, if specifically designated, there are obvious options - Irina, Boris, or the sitting Patriarch. Or a council - Ivan the Terrible had designated a regency council for Fyodor even though he was an adult.
De facto prime minister would obviously continue to be Boris, whether in his own name or as the right hand of his sister the Regent.
How would the boyars of Moscow behave during the next 5 years - OTL good years, as Autocratrix Feodosia grows from 5 to about 11?