The 43-year-old, from Reading, was arrested by Thames Valley Police, which is investigating the unexplained death of Gerald Jones.
Mr Jones, 51, died suddenly at an address in Wrenswood Close, Reading, on 19 June.
Police arrested the woman after receiving information following a post-mortem examination.
She was later released on bail until 30 January.

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Schalk went down in the box under no contact from Celtic's Erik Sviatchenko, with Liam Boyce converting the spot-kick to earn County a point.
Hearts' Jamie Walker was banned for a similar incident on the opening day of the season against Celtic.
And Tierney said: "It should be the same rule for every player."
Tierney was the player penalised in that match at Tynecastle in August, which Celtic won 2-1.
The champions paid a two-point penalty for Schalk's antics on Sunday, and Tierney could barely believe referee Don Robertson awarded a spot-kick as he thinks the incident was even worse than the one involving Walker.
"I knew straight away it was a dive," said Tierney, who scored Celtic's opening goal on Sunday. "It was the same kind of thing with Jamie Walker when we played Hearts in the first game of the season. But this incident was more obvious.
"It's not a nice part of the game, you can expect contact, but you're not going to go down if there's no contact. It's as simple as that.
"If it's striker's prerogative to do that then everyone would be falling about. Whenever you get close to people in games you need to stay on your feet, but if someone gets too close then fair enough.
"I couldn't believe it when the referee gave the penalty, everyone was so surprised. The linesman had a great view and was standing straight in line with it, but obviously not."
In the immediate aftermath of the incident, Celtic skipper Scott Brown was red carded for a late challenge on Boyce.
With Celtic likely to appeal against the red card, Brown will be available for Sunday's Scottish Cup semi-final against Rangers.
Boyce said: "I sort of knew that someone was coming, and I was waiting until the last second to try and get out of the way to buy a free-kick and take the pressure off.
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"Once I flicked it though I just felt like I'd been hit by a bus, and I looked down and my sock was ripped and my leg is really swollen now.
"I had been hit on the hand and got it sliced a wee bit and there were a few comments then, and just before that I had made a challenge from behind on him.
"These things build up in a game and I think he might have been a wee bit frustrated with the way things went and it has just happened."
A woman has been arrested on suspicion of murder after the death of a man in June.
[NEXT_CONCEPT]
Celtic defender Kieran Tierney reckons Ross County's Alex Schalk should be hit with a two-match ban for diving in Sunday's 2-2 draw in Dingwall.