Hello

I was trying to read a russian poem and I got some qeustions about it,

Зовут ее Светланою, (why the writer says Светланою? Is that a case? I know the name Светлана and have a feeling that Светланою is a declantion of it. Am I right? And why ее but not её ? Is it about a grammar rule or a typo?)

Как в песенке одной. (I understand this as "like in a song". Correct? Is песенке locative case of песня? I think it should be песня в песне. Is that right?)

Она всегда желанная,

В компании любой!

Thanks.